Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. A common type of inorganic particle used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays”. Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have exfoliation, wherein the polymer is fully dispersed with the individual nanometer-size clay platelets. Due to the general enhancement in air barrier qualities of various polymer blends when clays are present, there is a desire to have a nanocomposite with low air permeability; especially a dynamically vulcanized thermoplastic nanocomposite such as used in the manufacture of tires.
The preparation of elastomer-clay nanocomposites uses a number of methods to generate exfoliated clays. One of the most common methods relies upon the use of organically modified montmorillonite clays. Organoclays are produced through solution based ion-exchange reactions that replace sodium ions that exist on the surface of sodium montmorillonite with alkyl or aryl ammonium compounds. One of the deficiencies of this method is the limited thermal stability of the amines. A second is the lack of chemical bonding with the matrix, often leading to poor mechanical properties and increased hysteresis. A third is the negative impact that the release amines and degradation products have on the transport properties.
One method to improve the organoclay performance is to use functionalized polymers to treat the clay. This approach has been limited to materials that are soluble in water or to materials that can be incorporated into the polymerization reaction. This approach has been used to prepare nylon nanocomposites, using for example, oligomeric and monomeric caprolactam as the modifier. Polyolefin nanocomposites have utilized maleic anhydride grafted polyolefins to achieve some success in the formation of nanocomposites.
For example, it is known to utilize exfoliated-clay filled nylon as a high impact plastic matrix, such as disclosed in U.S. Pat. No. 6,060,549 to Li et al. In particular, Li et al. disclose a blend of a thermoplastic resin such as nylon and a copolymer of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene), the blend also including nylon containing exfoliated-clays that are used as a high impact material. Further, Japanese Unexamined Application P2000-160024 to Yuichi et al. discloses a thermoplastic elastomer composition which can be used as an air barrier. The nanocomposite in Yuichi et al. includes is blend similar to that disclosed in Li et al.
Nanocomposites have also been formed using brominated copolymers of isobutylene and para-methylstyrene. See, for example, Elspass et. al., U.S. Pat. Nos. 5,807,629, 5,883,173, and 6,034,164. It has been found that the efficiency of clay exfoliation is increased by increasing bromination level. Unfortunately these copolymers are very reactive and it is difficult to achieve high levels of functionalization without undue added vulcanization. Optimal performance in many applications requires the minimum level of vulcanization that yields acceptable physical properties, in that way aging and durability are maximized.
Thus, there is still a problem of achieving a nanocomposite suitable for an air barrier, in particular, an air barrier incorporating the copolymer (or “interpolymer”) of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene). While enhancing the impact properties and abrasion resistance of plastics such as polyamides, this copolymer tends to be a poor air barrier as compared with that of polyamide alone or other low-permeability plastic matrices. What is needed is an exfoliated nanocomposite of a halogenated copolymer of a C4 to C7 isomonoolefin, a para-methylstyrene and a para-(halomethylstyrene).